1. Field of the Invention
The present invention relates to a near infrared-cutting material to be laminated or combined with an engineering material such as electromagnetic wave-shielding material, antireflection material or the like for use as a front filter of a display device such as plasma display panel (PDP) or the like; as well as to a process for producing such a near infrared-cutting material. More particularly, the present invention relates to a near infrared-cutting material wherein the amount of the solvent remaining in the resin film containing a near infrared-absorbing dye, etc. is minimized and thereby the long-term stability of the near infrared-absorbing dye, etc. in the resin film at high temperatures is greatly improved, and a process for producing such a near infrared-cutting material.
2. Description of the Prior Art
There are known, for example, (1) a near infrared-absorbing filter produced by laminating, on a substrate, a composition which is a dispersion of a near infrared-absorbing dye in a binder resin, wherein the amount of the solvent remaining in the laminate is 5.0% by weight or less, specifically 0.05 to 3.0% by weight (see JP-A-2000-227515); and (2) a near infrared-absorbing panel produced by laminating a near infrared-absorbing layer (obtained by dispersing a near infrared-absorbing dye in a transparent high-molecular resin and then subjecting the dispersion to melt extrusion) with an electromagnetic wave-shielding layer having a near infrared-shielding ability and/or an electromagnetic wave-shielding ability (see JP-A-9-330612).
However, the above filter and the above panel have problems. With respect to the near infrared-absorbing filter (1), it is known as described in the literature that when the amount of the residual solvent is controlled at less than 0.05% by weight, the deterioration of the near infrared-absorbing dye during the long-term storage at high temperature and high humidity is small but the heat applied to achieve such a solvent level (less than 0.05% by weight) tends to deteriorate the near infrared-absorbing dye. That is, in the molded material obtained by coating, on a substrate, a composition (which is a dispersion of a near infrared-absorbing dye in a binder resin) and drying the resulting material, the stability of the dye in the resin film formed on the substrate is higher as the solvent level in the resin film is lower and, therefore, it is desired to reduce the solvent level to a possible lowest value (less than 0.05% by weight); however, the drying of the coated composition at atmospheric pressure incurs striking thermal deterioration of the near infrared-absorbing dye.
Thus, in the near infrared-absorbing filter (1), since the reduction in near infrared-absorbability and change of hue are occurring in the resin film of the molded material owing to the thermal decomposition of the near infrared-absorbing dye, it is impossible to achieve a residual solvent level of less than 0.05% by weight by increasing the temperature for drying or extendIng the time for drying; further, it is impossible to use a dye of high near infrared-absorbability but of low thermal resistance, making narrow the range of dye selection.
In the near infrared-absorbing panel (2), the near infrared absorbing-dye undergoes striking thermal deterioration (decomposition) during the melt extrusion at atmospheric pressure, and this dye decomposition reduces the near infrared-absorbability of the panel and also changes its hue. Therefore, the merit of the panel that the dye stability is high owing to no solvent use unlike in the near infrared-absorbing filter (1), is not utilized.
Also in the near infrared-absorbing panel (2), uniform dispersion of the dye is not easy and the color and near infrared-absorbability of the panel tend to be non-uniform; moreover, since the melt extrusion at atmospheric pressure is conducted ordinarily at high temperatures such as 240xc2x0 C. and the like, it is impossible to use a dye of high near infrared-absorbability but of low thermal resistance, making narrow the range of dye selection, as in the case of the near infrared-absorbing filter (1).
The present invention aims at providing (1) a near infrared-cutting material which has alleviated the above-mentioned problems of the prior art and wherein the amount of the solvent remaining in the resin film containing a near infrared-absorbing dye, etc. is minimized and thereby the long-term stability of the near infrared-absorbing dye, etc. in the resin film at high temperatures is greatly improved; and (2) a process for producing such a near infrared-cutting material.
The present invention provides:
a near infrared-cutting material produced by forming, on a transparent substrate, a transparent resin film containing at least a near infrared absorbing-dye and a dye having a maximum absorption wavelength at 550 to 620 nm, wherein the amount of the solvent remaining in the transparent resin film is 5 ppm by weight to less than 500 ppm by weight;
a near infrared-cutting material produced by forming, on a transparent substrate, a transparent resin film containing at least a near infrared absorbing-dye and a transparent resin adhesive layer containing at least a dye having a maximum absorption wavelength at 550 to 620 nm so that the transparent resin adhesive layer becomes the outermost layer, wherein the amount of the solvent remaining in the transparent resin film and/or the transparent resin adhesive layer is 5 ppm by weight to less than 500 ppm by weight; and
a process for producing a near infrared-cutting material, which comprises coating, on a transparent substrate, a transparent resin solution containing at least a near infrared absorbing-dye and a dye having a maximum absorption wavelength at 550 to 620 nm, drying the resulting material at atmospheric pressure until the amount of the solvent remaining in the formed film becomes 3% by weight or less, and then drying the resulting material under reduced pressure until the amount of the solvent in the film becomes 5 ppm by weight to less than 500 ppm by weight.